Investigators are piecing together the life of the 23-year-old Nigerian student charged with trying to blow up an American airliner on Christmas Day. They know he spent time in Yemen. They know he attended an Arabic language school from August until early December of this year. They think he may have picked up the explosives used in the attack while he was there. And now they're trying to establish his connection with a controversial U.S.-born imam, the same imam who was linked to the November attack at Fort Hood.

NPR's Dina Temple-Raston reports.

DINA TEMPLE-RASTON: If Anwar al-Awlaki's name sounds vaguely familiar, it should. He ended up as a prominent player in last month's Fort Hood shooting. FBI investigators say the accused shooter in that attack, Army Major Nidal Hasan, emailed the radical imam in Yemen asking his advice. A short time later, Hasan allegedly went on a rampage that killed 13 people.

If you heard Awlaki's sermons on the Internet, you might initially think there's some mistake. They don't sound all that fiery. In fact, his voice - as heard here in one of his Internet sermons - is rather sweet.

Imam ANWAR AL-AWLAKI: Some people say that our relationship with the people of the book should be a relationship based on peace and dialogue.

TEMPLE-RASTON: But the soft-spoken demeanor belies a violent message. His most influential lecture is called "Constants on the Path to Jihad," or "44 Ways to Jihad," and it's become a road map for lone wolf jihadists.

Imam AL-AWLAKI: Whenever you see the word terrorist, replace it with the word mujahid. Whenever you see the word terrorism, replace it with the word jihad.

TEMPLE-RASTON: What he's saying is attacks and killings that the rest of the world considers terrorism, he sees as perfectly legitimate. Typically, in his Internet sermons, Awlaki reads from the Quran in Arabic.

Imam AL-AWLAKI: (Arabic spoken)

TEMPLE-RASTON: And because many of his followers don't speak Arabic, he interprets the passages for them.

Imam AL-AWLAKI: When the forbidden months are past, then fight and slay the pagans wherever you find them and seize them, beleaguer them and lie in wait for them in every stratagem of war.

Professor SAM RASCOFF (New York University School of Law): Because he has a kind of unusual ability to interlace an appealing familiar American preacher style with a fairly vitriolic message.

TEMPLE-RASTON: Sam Rascoff used to be in charge of terrorism intelligence analysis at the New York Police Department. He says Awlaki is targeting young men searching for guidance - young men like bombing suspect Umar Farouk Abdulmutallab.

Prof. RASCOFF: To listen to Awlaki is to feel like one's in the company of someone who understands you, who understands your social predicament and who literally and figuratively speaks your language.

TEMPLE-RASTON: Investigators haven't said definitively that the two men met, but they say, privately, the two were in contact. They're also combing through hundreds of Internet postings they believe were written by Abdulmutallab. The username attached to the account, Farouk1986, matches his middle name and birth year. And some of the timing and details in the writings track where Abdulmutallab was at the time.

The Internet postings begin in 2005, and they're clearly written by a lonely young man. One post in 2005 read: I'm in a situation where I do not have a friend. I have no one to speak to. I don't know what to do. Abdulmutallab was young, didn't speak Arabic very well and was looking for religious guidance on the Internet. In other words, he was Awlaki's target audience.

Professor BRUCE HOFFMAN (Terrorism Expert, Georgetown University): His facility with English has given him that kind of link that he's become sort of the favored source.

TEMPLE-RASTON: Bruce Hoffman is a terrorism expert at Georgetown University. He says Awlaki's list of followers reads like a who's who in the jihadist world. He's linked to two of the September 11th hijackers, a group of Canadian Muslims who were charged with plotting attacks on the Parliament building in Ottawa, six men who wanted to attack Fort Dix in New Jersey and the so-called London subway bombers.

Prof. HOFFMAN: But I think it awaits further investigation to see whether he was doing it on his own or whether he was following the instructions or guidance or direction of others.

TEMPLE-RASTON: Awlaki moved to Yemen in 2002. Investigators are trying to determine if Abdulmutallab went to Yemen specifically to visit him and whether Awlaki played any role in introducing him to the people who may have provided the explosives for Northwest Flight 253.

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